Formulation of Time-Domain Random-Walk Compartment Model for Radionuclide Migration from a Geologic Repository

A method that utilizes a time-domain random-walk model with residence time distributions (RTDs) for radionuclides in a compartment has been developed and applied to a safety assessment model for geologic disposal of high-level radioactive wastes. By choosing a proper RTD, which can be determined by a detailed model for radionuclide transport in a compartment, the present compartment model can simulate radionuclide transport through a repository region without numerical dispersion due to coarse discretization. The method has been demonstrated and illustrated for the case that the physical transport processes in a compartment and the corresponding RTD are known. For an actual performance assessment for a geologic repository, in which multiple waste packages are placed in an array configuration, it is considered that the repository-scale transport simulation can be greatly modularized and simplified by obtaining an RTD around a single package.